Placental Pathology II: Examination and Future Pregnancies

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Check out this article from Contemporary OB/GYN on placental pathology to augment your learning: https://www.contemporaryobgyn.net/view/placental-pathology-it-time-get-serious 

What do they look for on the placenta anyway? 

  • Gross examination of the placenta - remember, we aren’t pathologists! 

    • Fresh examination is usually best

      • Why?  Because you can send cultures, cytogenetic studies, and injections of the vessels on fresh, but not fixed, specimen

    • Umbilical cord 

      • General appearance: will comment on color, nodules, strictures, edema, and coiling 

      • Will also discuss area of placental insertion (ie. velamentous, marginal, etc) 

      • Length + knots 

      • Vessels - single or two UAs? 

      • Other things: hematomas, neoplasms, cysts 

    • Membranes 

      • Color

      • Insertion of the umbilical cord in membrane or on placenta? 

    • Placental parenchyma 

      • Usually will comment on weight and percentile for gestational age

        • Some correlation with birth weight  

      • Dimension and appearance - also, is it bilobed? Are there succenturiate lobes? 

      • Maternal surface: should be complete when looking at it grossly 

        • Can also see areas of infarcts

      • Fetal surface: review if there are large vessels coursing near the edge, if there are cysts, subchorionic hematomas, etc 

So what are some common findings, and what should we look for on the report? 

  • Placental weight 

    • Some type of chronic stress may lead to smaller placentas

      • Think chronic hypertension, diabetes, etc

      • Usually can product placentas that are <10th%ile  

    • Some pitfalls: there are conditions that lead to fetal stress that can also make placentas abnormally large, ie. hydrops 

  • Infarctions, vessel artherosis

    • Often, these are findings that are related ot hypertensive disorders of pregnancy 

    • Can see things like fibrinoid necrosis of the vessel wall, perivascular infiltrates of WBC; also can see infarcts

    • Can also see areas of abruption: but remember, abruption is a clinical diagnosis! 

      • This is because there can be small area of bleeding, placenta infarct etc that are not clinically relevant 

      • Under the microscope, abruption would appear as diffuse retromembranous or intradecidual hemorrhage, irregular basal intervillous thrombi, and recent villous stromal hemorrhage 

      • However, this is not specific, and can be seen with normal delivery as well 

  • Infection

    • I feel like I often see “chorioamnionitis” written all over the reports, even when the patient doesn’t have chorio! So what do the pathologists see? 

    • Histopathologic findings are neutrophilic inflammation of the chorion and amnion 

    • You can also see inflammatory infiltrate of the vascular portion of the umbilical cord or Wahrton’s jelly 

    • The pitfall: 

      • Clinically diagnosed chorio may not always been seen on histology and vice versa! Why is that? 

      • Clinically: it is possible that there was another inflammatory process going on, or chorio was diagnosed by maternal fever, which can be caused by many other things (ie. misoprostol, epidural use) 

      • Histologically: Remember that evidence of inflammation on histology does not always mean that there is microbiologic evidence of infection; cultures of amniotic fluid or membranes do not document a bacterial infection in 25-30% of placentas with histologic chorio 

So how does this affect our practice or the patient’s future pregnancies? 

  • There is some data that suggests that some placental pathologies can lead to recurrence of poor outcomes in pregnancy 

    • For example, one study showed that inflammation in the placenta were associated with recurrent preterm birth and spontaneous preterm birth 

      • Ie. Villitis 

    • There is also some suggestion that chronic endometritis can lead to recurrent miscarriages 

    • The current issue is that while research has shown these associations, there isn’t anything currently that has proven to clinically improve outcomes

    • Though this does spark some interesting debate about tamping down inflammation: since there is some observation that the use of antenatal steroids seems to temporarily improve preeclampsia 

    • This is all just speculation though, and doesn’t mean we recommend using chronic steroids to prevent preeclampsia! 

    • So… not a super satisfying answer  

  • Other predictions 

    • With regards to abnormal placentation such as placenta accreta spectrum, there is a 25-30% recurrence risk based off of findings of histological examination of the placenta 

    • I’m not convinced this is clinically useful, unless during delivery, there was not a diagnosis of accreta 

    • Certainly, if there is focal accreta diagnosed clinically, I think clinically, we would also counsel the patient about increased recurrence risk 

  • What placental pathology can’t do 

    • The literature suggests that widespread pathologic examination of the placenta does not prognosticate adverse childhood and neurologic outcomes 

    • In some selected cohorts though, there can be some associations 

  • Another thing to know is that findings on the placenta can give patients closure on things like poor outcomes

    • Placenta pathology can be very useful in determining the etiology of stillbirth, particularly after 24 weeks gestation 

    • Studies show that placental examination was useful in up to 64% of cases of stillbirth (compared to only 12% for karyotype and 0.4% for parvo testing) 

    • However, we need to recognize that while this may give patients closure, it is not necessarily predictive of future pregnancies 

  • The medical-legal realm 

    • People may ask if we can refute a legal claim after examination of a placenta 

    • We are not lawyers 

    • However, a Green Journal article that looked broadly in the literature about placental examinations showed that there was anecdotal evidence at best about placental pathology refuting cases of adverse childhood neurologic status 

    • In one analysis of 209 malpractice claims, only 2 cases were claimed to have been successfully defended by evidence gained through placental examination alone